1. Field of the Invention:
The present invention relates to a method for fabricating a semiconductor device and, more particularly, to a method for (quasi-)anisotropic etching of silicon-based material in single- or poly-crystalline form. The etching process according to the present invention employs substantially no plasma.
2. Description of the Related Art:
The demand for finer patterns of semiconductor integrated circuits has led to the development of a variety of dry etching processes. The fabrication of finer patterns with a high aspect ratio (width-to-height ratio) needs the technique of anisotropic etching (that takes place selectively in the vertical direction). The anisotropic etching is used for microfabrication of silicon-based material such as semiconductor substrate, gate electrode, and interconnect.
Conventional anisotropic etching employs plasma which ionizes a fluoride gas such as CF.sub.4 and SF.sub.6, thereby generating active fluorine species which react with silicon to give volatile silicon fluoride. A disadvantage of this conventional process is the possibility of carbon or sulfur in the etching gas combining with silicon and entering the semiconductor element during etching. Another disadvantage is that the etching gas deposits a teflon-like polymer on the inner wall of the chamber after etching for a long period of time. In addition, plasma for etching causes damage to semiconductors, presenting a problem with reliability.
The conventional process for etching silicon-based material employs fluorinated halogen as an etching gas, which is a substance represented by the formula XF.sub.n (wherein X is a halogen other than fluorine, and n is an integer), such as ClF, ClF.sub.3, BrF, BrF.sub.3, IF, and IF.sub.3. These substances have such a strong fluorinating action that they perform etching (gas etching) without requiring active species generated by plasma. Gas etching, like wet etching, advances in the lateral direction as well as in the vertical direction. In other words, it does not perform anisotropic etching which advances only in the vertical direction.